1. Field of the Invention
The present invention relates to disposable medical electrodes for use with electromedical equipment which applies electrical stimulation through the patient's skin.
2. Description of the Prior Art
Medical electrodes which are attached to the skin of a patient have been used for many years. With the ever-increasing sophistication of medical electronics, medical electrodes are continually finding new and wider uses. One common type of medical electrode may be termed a "monitoring" electrode, which is used in conjunction with monitoring equipment such as electrocardiogram (EKG) and electroencephalograph (EEG) equipment. These monitoring electrodes are typically used in sensing voltages, and the current levels are quite low. Due to the low current density encountered, the area of electrical contact between the monitoring electrode and the patient's skin can be relatively small without danger of damage to the patient's skin.
A transmitting or stimulating electrode for use with a transcutaneous electrical nerve stimulator (TENS) device of similar electromedical equipment is used for the introduction of electrical current into the patient's body. Since the electrical currents applied are much larger than those encountered with monitoring electrodes, the stimulating electrode must provide a relatively large area of contact with the patient's skin so that the current density of the electrical current being applied is low enough that it does not damage skin tissue. This requires that the conductivity across the entire area of the electrode be relatively high, so as to distribute the current over a relatively large area of skin. In addition, local "hot spots" of nonuniform (higher) current density must be avoided.
In the case of a stimulating medical electrode used with TENS devices, the electrode is typically applied by the patient without the assistance of medical personnel. As a result, it is important that the electrode be very simple and convenient to use.
Since TENS devices are typically used for treatment of chronic or long term pain, the electrodes used with TENS devices must be capable of remaining on the patient's body for prolonged periods of time (several days or more). The electrode must adhere well to the patient's body despite normal physical movement and normal activities such as bathing.
In the past, reusable TENS electrodes have been widely used. These reusable electrodes normally require application of an electrically conductive gel or paste to ensure electrical contact between the electrode and the patient's skin.
Considerable effort has been devoted to the development of a disposable TENS electrode which can simply be discarded after a single use, and which is easier and more convenient to use than a reusable electrode. Because it is intended to be discarded after a single use, the disposable electrode should be of very low cost.
Unfortunately, the prior art disposable TENS electrodes have had several disadvantages. First, the disposable TENS electrodes typically have had a small electrically active area, which tends to cause high current densities through the patient's skin. This can result in a higher incidence of skin irritation.
Second, those prior art disposable TENS electrodes which are self-adhesive (i.e. the adhesive to the skin is an electrical conductor) have been less than satisfactory. The self-adhesive electrode typically is either eccessively aggressive and debrides the skin, or is nontacky and tends to fall off the patient's skin. The development of an adhesive having the combination property of uniform consistent electrical conductivity over a significant surface area and a sufficiently tacky surface to hold the electrode on the patient's skin has proved to be an extremely difficult technical problem.
Third, the prior art disposable TENS electrodes have been expensive, due to complexity in manufacturing and high cost of materials. These high cost factors have been the result of the need to avoid hot spots and to provide a disposable electrode which has both excellent adhesive properties and high, uniform electrical conductivity.
Fourth, some prior art disposable electrodes have suffered from a lack of biocompatibility (skin irritation). These disposable electrodes have involved direct metal contact with the skin, or have used a foam soaked in a wet ionic conductor.
There is a continuing need for an improved electrode for use with TENS devices and other electromedical equipment which applies electrical current to the patient's body through the patient's skin. In particular, there is a need for an inexpensive disposable TENS electrode which is easily manufacturable, is easy and convenient to use without the assistance of medical personnel, and provides uniform current density so that the danger of skin irritation or damage is minimized.